Mordant N, Delour J, Léveque E, Arnéodo A, Pinton J-F
Laboratoire de Physique, Ecole Normale Suprieure de Lyon, 46 allée d'Italie, France.
Phys Rev Lett. 2002 Dec 16;89(25):254502. doi: 10.1103/PhysRevLett.89.254502. Epub 2002 Dec 3.
Using a new experimental technique, based on the scattering of ultrasounds, we perform a direct measurement of particle velocities, in a fully turbulent flow. This allows us to approach intermittency in turbulence from a dynamical point of view and to analyze the Lagrangian velocity fluctuations in the framework of random walks. We find experimentally that the elementary steps in the walk have random uncorrelated directions but a magnitude that is extremely long range correlated in time. Theoretically, a Langevin equation is proposed and shown to account for the observed one- and two-point statistics. This approach connects intermittency to the dynamics of the flow.
利用一种基于超声波散射的新实验技术，我们在完全湍流中对粒子速度进行了直接测量。这使我们能够从动力学角度研究湍流中的间歇性，并在随机游走的框架内分析拉格朗日速度涨落。我们通过实验发现，游走中的基本步具有随机不相关的方向，但步长的大小在时间上具有极长程的相关性。从理论上提出了一个朗之万方程，并证明它能解释所观察到的单点和两点统计特性。这种方法将间歇性与流动动力学联系了起来。
